The receiver side of an optical data communication system is typically comprised of an optical fiber, electrical connectors, an optical-electronic interfacing circuit, and a destination integrated electronic processing circuit. One main element in the electronic interfacing technology is a light sensor, which is used to detect the incoming optical signal. The optical signal can be contained in one specific frequency band after optical filtering, as in wavelength division multiplexing (WDM), or it can be unfiltered and composed of various wavelengths. The light sensor (e.g., photodetector) converts the detected light into electrical current to be used by the destination integrated electronic processing circuit.
Typically, the light sensor is separated from the processing integrated circuit and is connected to both the optical fiber and the integrated circuit. Light sensors, such as, but not limited to, InGaAs photodetectors, are costly and require a manufacturing process that differs from the process for manufacturing the electrical chip. In addition, the material used for such photodetectors may be costly. Therefore, use of the photodetectors, as a separate discrete component, adds manufacturing time and manufacturing cost to the completion of an optical receiver.
In addition to the abovementioned, the computational speed of the integrated circuit chip is limited by the frequency response of the photodetector. In other words, if the computational speed of the chip is faster than the frequency response of the photodetector, the complete system's computational speed will be equal to the lower value, that of the photodetector.
Photodetectors have been manufactured using, for example, Germanium epitaxially grown on Silicon. Because Germanium has a smaller bandgap than Silicon, these photodetectors detect radiation of infrared photons. Such photodetectors typically exhibit responsivity between 0.2 and 0.4 A W−1 and frequency response of 2 gigahertz or less, but exhibit very poor response for wavelengths greater that 1.5 micrometers. If the photodetector were one hundred percent efficient the photoresponse would be 1.25 A W−1 for 1.5 micrometer radiation. The Germanium photodetectors require thermal cycles that are difficult to incorporate in CMOS processing. Others have created Silicon photodetectors using ion implantation, however their devices have limited frequency response of approximately 2 MHz and weakly absorb the radiation, resulting in reduced photoresponse. Unfortunately, these photodetectors still do not have a fast enough frequency response and suffer processing damage at temperatures above 200 C, which are required for CMOS processing.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.